The proposed research addresses the central immunosuppressive mechanism(s) generated by daily exposure to N-Nitroso-dimethylamine (DMN). It has been previously demonstrated that DMN is toxic and carcinogenic to a variety of animal species. The effects appear to be mediated by metabolites generated in the enzymatic oxidation of DMN by the liver resulting in the formation of alkylated nucleic acids. Other alkylating agents like cyclophosphamide have been shown to be potent immunosuppressants, few studies unfortunately have established the relationship between exposure to DMN and alterations in the immune response. Preliminary results have demonstrated a decrease in cell-mediated immunity as a result of changes in macrophage (M0) function. This proposal will determine the suppressive effects of DMN using purified immunocompetent cells in defined functional assays and identify the molecular mechanisms(s) responsible for this induced alteration. Experiments outlined will establish how daily exposure of animals to DMN compromises T-lymphocytes, or M0 populations in number, ectoenzyme profiles, expression of phenotypic markers, and function in cell-mediated responses. These studies will include reconstitution of T lymphocyte antigen and mitogen responses; induction of delayed typed hypersensitivity and mixed lymphocyte reactions, and tumorcidal assays. Bone marrow from DMN treated animals will be grown with colony stimulating factor to determine the effects on the in vitro generation of M0 populations using the above outlined functional assays. The relationship between the cellularity, DNA synthesis, cell-cycling, ectoenzyme profile and expression of Ia antigens will also be established. Although results suggest an immunosuppressive component(s) found on the serum or liver homogenates from DMN treated animals is responsible, additional experiments will establish the effects of direct DMN exposure. Another major thrust will be to identify the DMN induced mediator(s) responsible for modulation of M0 maturation. This will entail isolation from the liver homogenates and serum samples followed by biochemical analysis using established methodologies. These studies also permit delineation of the immunosuppressive nature of the hepatocarcinogen DMN at the molecular, cellular and animal level and how such toxic compounds compromise immune responsiveness.